The accurate detection of particles, including photons, molecules, electrons, ions and phonons, is essential to many industrial and research measurements. X-ray microcalorimeters convert the x-ray energy into heat in the form of hot-electrons or phonons. An x-ray microcalorimeter consists of an absorber to stop and thermalize incident x-rays and a thermometer to measure the resulting temperature rise. The first x-ray microcalorimeters used insulating or superconducting absorbers (for low heat capacity) and a semiconductor thermistor thermometer. While these achieve adequate energy resolution (7.1 eV FWHM at 6 keV), the response time is intrinsically slow. A known X-ray microcalorimeter uses a normal-metal absorber and a NIS tunnel junction to measure the temperature rise. The response is fast, but the best achieved energy resolution is 18 eV FWHM at 6 keV.
Superconducting transition-edge sensors have been proposed for use as a thermometer within an x-ray microcalorimeter. The temperature of a superconducting film is held within the superconducting transition, and heat deposited in the film is measured via the strong temperature dependence of the film's electrical resistance in this region. For x-ray detection the optimum transition temperature is between about 50 and 150 mK. The choice of the T.sub.c within this range depends on the desired detector parameters. Superconducting tungsten films having T.sub.c =70 mK have been used for x-ray detection. For an elemental superconductor such as tungsten, the transition temperature tends to be a fixed property of the metal and is difficult to tune to suit specific applications. For alloys of superconductors with normal metals, the T.sub.c can be adjusted, but the transition edge is not sharp, and the alloys are not stable. The transition temperature can also be adjusted via the proximity effect in superconductor/normal-metal bilayers. When a clean interface is made between a superconducting film and a normal-metal film, and the films are thinner than the relevant coherence lengths, the bilayer acts as a single superconducting film with a transition temperature suppressed from that of the bare superconductor. By varying the relative film thickness, the T.sub.c of the bilayer can be adjusted. Iridium/gold bilayers have been described for particle detection. The T.sub.c of elemental iridium is 112 mK, which is within the target range for x-ray detection. However, the Ir/Au system is very difficult to reproducibly fabricate. It requires the substrate to be heated, it requires a very clean, high vacuum deposition system, and the transition temperature of such bilayers is limited to less than 112 mK. Other bilayer systems have been developed using an aluminum/normal-metal bilayer that have a larger tunable transition range, that are more easily deposited, that are deposited without heating the substrate, that are deposited in a deposition system with only moderate vacuum (.about.1e-7 torr, .about.1e-7 millimeter mercury, to .about.0.019336 pound force per square inch, .about.-931 Pa), that are more reliably reproducible, and that are sharper superconducting transitions. Aluminum/normal-metal bilayers have been used as TES's since they have reproducible transition temperatures. The T.sub.c can be reduced by more than an order of magnitude, the T.sub.c is tunable in a predictable fashion as a function of the thicknesses of the individual layers, and the transition edge is extremely sharp.
During operation the TES is maintained within the transition region by electrothermal feedback (ETF). The transition from the superconducting to the normal state is measured to determine the energy deposited in the system by particles. The bilayer resistance can be monitored by voltage biasing the bilayer and measuring the current through the bilayer, for example with a superconducting quantum interference device (SQUID). The increase in bilayer resistance with temperature leads to a reduction in measured current. With an ETF-TES the energy deposited in the bilayer is approximately the integral of the reduction in feedback Joule heating, or the bias voltage multiplied by the integral of the change in measured current. Alternatively the bilayer resistance can be monitored by current biasing and measuring the voltage across the bilayer with a FET. There is a continuum of biasing conditions between voltage biasing and current biasing which can be used in the measurement. The superconducting transition can also be measured, for instance, via the change in the self or mutual magnetic inductance of a coil or coils placed around the bilayer, or by a kinetic inductance measurement.
Representative of the art is:
U.S. Pat. No. 5,641,961 (1997) to Irwin et al. discloses a superconducting transition edge detector using electrothermal feedback. The sensor comprises a primary heat sink such as a substrate, a variable resistor made of a superconducting material deposited on the substrate, and a current sensing means such as a SQUID array for measuring the current through the variable resistor. The resistor is voltage biased, and the bias voltage is chosen such that the resistor is maintained within its superconducting transition region by electrothermal feedback.
U.S. Pat. No. 5,610,510 (1997) to Boone et al. discloses a that granular film [multiple Josephson junction] detectors display nonbolometric behavior which is presumably caused by weak links. Boone further discloses that a nonbolometric mechanism may be a better means of making a detector, particularly for microwave frequencies.
U.S. Pat. No. 5,571,778 (1996) to Fujimoto et al. discloses a superconductor junction material which comprises a substrate of a single crystal, and at least one flux flow element, and optionally at least one Josephson junction element, provided on the surface, each of the flux flow and Josephson junction elements being formed of a superconducting oxide layer having a weak link.
U.S. Pat. No. 5,552,375 (1996) to Nishino et al. discloses a method of forming superconducting devices including a type having a structure of a superconductor--a normal conductor (or a semiconductor)--a superconductor, and a type having a superconducting weak-link portion between superconductors.
U.S. Pat. No. 5,532,485 (1996) to Bluzer et al. discloses a multispectral superconductive quantum detector. Each quantum detector is connected to a read-out loop [SQUID] which includes superconductive material that defines a path. The SQUID read out of the superconductive quantum detector is using a direct coupled approach. A SQUID bias current I.sub.SQ is needed to cause the SQUID to maintain proper operation of the SQUID in the voltage state.
U.S. Pat. No. 5,356,870 (1994) to Fujiwara et al. discloses an ion beam irradiated to an oxide superconducting thin film formed on a substrate to disturb the crystal structure of the superconducting thin film and thus forming a damaged layer.
U.S. Pat. No. 5,331,162 (1994) to Silver et al. discloses a sensitive, low-noise, superconductive infrared photo detector. Each detector element includes a thin granular film of superconducting material which forms a randomly-connected array of weakly coupled superconductors. The weakly coupled superconductors promote the formation of oppositely polarized fluxons which are driven toward opposite sides of the film when subjected to the bias current. The detector array is connected to a current source, and a SQUID read-out circuit.
U.S. Pat. No. 5,219,826 (1993) to Kapitulnik discloses a superconducting Josephson junction created in high T.sub.c superconducting film with a bridge connecting two superconducting banks by subjecting the bridge to a tunneling electron current from a sharp electrode close to the bridge.
U.S. Pat. No. 5,179,072 (1993) to Bluzer discloses a multispectral superconductive quantum radiant energy detector and related method utilizing a closed loop of superconductive material having spaced legs, one of which is disposed to ambient.
U.S. Pat. No. 5,126,315 (1992) to Nishino et al. discloses a superconducting device including a type having a structure of a superconductor--a normal conductor (or a semiconductor)--a superconductor, and a type having a superconducting weak-link portion between superconductors.
U.S. Pat. No. 5,021,658 (1991) to Bluzer discloses a superconducting infrared detector. The detector is also connected to a SQUID amplifier. The SQUID amplifier is connected to a bias current source so that its output voltage is a function of the flux coupled to the SQUID. The electrical connections disclosed in this patent are analogous to the described invention.
U.S. Pat. No. 5,019,721 (1991) to Martens et al. discloses active superconducting devices formed of thin films of superconductor which include a main conduction channel which has an active weak link region.
U.S. Pat. No. 4,983,971 (1991) to Przybysz et al. discloses a superconducting analog-to digital converter for producing a digital output signal which is a function of an analog input signal.
U.S. Pat. No. 4,970,395 (1990) to Kruse, Jr. discloses a phonon detector based upon phonon-assisted tunneling in superconductor-insulator-superconductor or super-Schottky structures in which the superconductor is a high-transition temperature superconductor.
U.S. Pat. No. 4,831,421 (1989) to Gallagher et al. discloses a switch that introduces quasiparticles at an asymmetric location into a reduced cross-sectional area microbridge link that is part of an output path.
U.S. Pat. No. 4,578,691 (1986) to Murakami et al. discloses a photodetecting device having Josephson junctions, comprising an insulating substrate, a polycrystalline superconductor film formed on the insulating substrate such that Josephson junctions are formed at grain boundaries.
U.S. Pat. No. 4,521,682 (1985) to Murakami et al. discloses a photodetecting device having Josephson junctions, comprising an insulating substrate, a polycrystalline superconductor film formed on the insulating substrate such that Josephson junction are formed at grain boundaries.
U.S. Pat. No. 4,096,508 (1978) to Fulton discloses a supercurrent memory device comprising a plurality of extended Josephson junctions coupled to one another by having their weak-link layers in contact.
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The foregoing TES's are deficient from the disclosed invention in a number of ways. The deficiencies are satisfied by the present invention. What is provided is a TES having a weak link to reduce noise due to phase slip line motion and irreproducibility. What is provided is a TES having a step edge weak link. What is provided is a TES having a thinned weak link. What is provided is a TES having a perforated weak link. What is provided is a TES having a reduced T.sub.c weak link. What is provided is a TES having impurity weak links. What is provided is a TES having multiple weak links.